The dielectric relaxation of polar-molecule reaction with linear reaction dynamics is studied via the reaction-diffusion equation in the spherical coordinate (the modified Smoluchowski-Debye equation) based on the self-consistent field approximation. The polarization of two kinds of reaction systems, the interacting system and the polarizable system, is derived. In the interacting system, the interaction of the polar molecules is dependent on the concentration of the molecules, resulting in the complex interacting behavior of the polarization process. In the polarizable system, the anisotropic polarizability gives rise to the complex behavior of the third harmonic.